Encapsulated switch having structure for preventing unwanted thermoelectric transients



G. W. PLICE UNWANTED THERMOELECTRIC TRANSIENTS Filed Oct. 11, 1965 ENCAPSULATED SWITCH HAVING STRUCTURE FOR PREVENTING March 7, 1967 INVENTOR GERALD VV. PLICE No.. :o

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ATT@ RNEY United States Patent Office 3,308,4@8 Patented Mar. 7, 1967 ENCAPSULATED SWITCH HAVING STRUC- TURE FOR PREVENTING UNWANTED THERMELECTRIC TRANSIENTS Gerald W. Plice, Morton Grove, Ill., assignor to James Electronics, Inc., a corporation of Illinois Filed Oct. 11, 1965, Ser. No. 494,713 6 Claims. (Cl. 335-151) v This invention relates generally to electric relay switches, and particularly to a switch having structure for preventing unwanted thermoelectric transients.

One of the problems attendant upon the use of any device for switching small signals is that of introducing unwanted voltages arising from the heating effect at junctures made of dissimilar metals, such as iron-copper junctures for example. Switching devices of the type comprised of magnetic reed material encased in a glass envelope and driven by a coil surrounding the envelope are valuable for interrupting very small voltages and are low in cost, have long lives and high reliability. However, when used in circuits of low signal Value, the necessary dissimilar metal junctions can give rise to thermoelectric E.M.F.s comparable in magnitude to that of the signal being switched. It is to the elimination of such unwanted transients arising from a heated ambient or milieu that this inven-tion is particularly directed.

According to the invention, one or more reed switches are housed within a bobbin supporting an exterior driving coil for the reed switches. The latter have their terminal members, which may be of nickel-iron, soldered or otherwise connected to lead wires of a dissimilar metal, the lead wires in turn being connected to mounting pins or prongs for mounting the structure on a conventional chassis. The ends of the bobbin are provided with closures to seal the interior thereof, and the cavity within the -bobbin is filled with a suitable dielectric coolant, such as one within the Freon series.

The dielectric coolant insures that there is no substantial thermal difference between the junctures of dissimilar lmetals atopposite ends of the reed switches, and the presence of the very line leads connecting the junctures to their respective prongs insures that substantially mini mal heating effects are transmitted to the dissimilar junctures, all to the end that substantially no thermoelectric effe-cts are introduced into the system.

With the foregoing considerations in mind it is a principal object of this invention to provide an improved electromagnetic switch characterized by structure substantially minimizing any thermoelectric effects.

Another object is to provide an encapsulated magnetic reed switch having structure substantially eliminating the transmission of heat to the dissimilar junctures provided for connecting the reed elements to exterior circuitry, and to provide structure whereby substantially no differential heating effect exists across the opposite dissimilar circuit connections thereof.

In the drawing:

FIG. 1 is a longitudinal cross section through an encapsulated switch having the improvements according to the present invention embodied therein;

FIG. 2 is a vertical longitudinal section taken along the line 2 2 of FIG. 1 looking in the direction of the arrows;

FIG. 3 is a transverse section taken along the line 3 3 of FIG. 2;

FIG. 4 is a view somewhat similar to FIG. 2 showing an alternate embodiment of the invention;

FIG. 5 is a view similar to FIG. 1 showing still another embodiment of the invention;

FIG. 6 is a vertical longitudinal section taken along the line 6 6 of FIG. 5 looking in the direction of the arrows; and

FIG. 7 is a transverse section taken along the line 7 7 of FIG. 6.

Referring now particularly to FIGS. 1 to 3 of the drawing, the improved switch according to one embodiment of the present invention is referred to by the reference numeral 10 and includes a plurality of glass envelopes 11, generally cylindrical in form and tapered as at 12 at their ends. Each end of the envelope 11 has sealed thereto conductor members 13 and 14 connected internally of the glass envelope 11 to respective reeds 16 and 17. The lat-ter are made of electrically conducting magnetic material, and are connected to the conductor members 13 and 14 by soldering or welding. The envelope 11 is generally evacuated of air or other gas to provide sensitive movement of the reeds 16 and 17 therein.

Each of the envelopes 11 is supported within a hollow bobbin 1S, and the same may be formed with hollow center 19 of rectangular cross section. Upper and lower panels 21 and 22 defining the hollow center 19 are provided with paired longitudinally extending lands 23, as seen in FIG. 3, these lands 23 providing supports for the glass envelopes 11.

The hollow bobbin 18 is provided at each end with an end wall 24, each such end wall 24 having contact members 26 molded integrally therein, each contact member being adapted to be connected to a correlative conductor member 13 or 14 of capsule 11, as the case may be.

The contact members 26 are connected to conductor member 13 or 14 by a conductor 27 of very small cross section as compared to the cross section of conductor member 13 or 14 and 'contact member 26, and is substantially incapable of transferring heat from contact member 26 to conductor members 13 and 14.

The bobbin 18 is adapted to have a driving coil 28 wound thereon between the end walls 24, coil 28 upon energization thereof closing reeds 16 and 17 on each other to complete a circuit in a Awell known fashion.

The hollow center 19 of hollow bobbin 18 is closed 'by end caps 29 threaded at 31 to end threaded ferrnles 32 extending from the ends of .bobbins 18. Gaskets 33 are interposed between end lcaps 29 and the ferrules 32 to seal the interior 19 of bobbin 18. A suitable dielectric coolant DE fills the interior of the bobbin 18.

By reason of the dielectric coolant and the size of the conductor 27, a number of desirable properties are provided *by the switch thus far described. At the junc- -ture of the cond-uctor 27 to the conductor member 13 or 14 and to the contact member 26 metals of dissimilar kind are connected. This may be done by soldering or welding and the presence of heat at such juncture gives rise to the creation of a thermoelectric transient. By reason of the very small cross section of conductor 27 as compared to contact member 26 there is substantially no heat sink effect from contact member 26 to any juncture of dissimilar metals within the structure 10. The creation of substantially no thermoelectrictransients, by reason of the presence of the dielectric coolant within the bob-bin 18, the existence of a thermal difference between spaced dissimilar connections is kept to a minimum. The assembly described may be housed within a suitable can 29 in a manner well known in the art.

Referring now to FIG. 4, there is shown another form of the invention in which the hollow center 19 is closed by end caps 36. These are resilient and are forced into position by a snap action over a snap flan-ge 37 on the end wall 24 against a gasket ring 38.

Referring now to FIGS. 5 t-o 7 of the drawing, there is shown another embodiment of the invention indicated 'by the reference numeral 40. In this embodiment, the glass envelopes 11 have their tapered ends 12 held in 3 apertures 41 in end walls 42 flanking a rectangular cross section winding bobbin 43 for coil 28.

The connections of the conductor members 13 and 14 to contact members Z6 are made as previously described, but inI this case the contact members 26 are embedded in 4base 44 of a Walled capsule 46. Bobbin 43 together with end walls 42 and envelopes 11 is adapted to be supported in a cavity 47 in base 44. When the assembly thus tar described is completed and cavity 48 in capsule 46 is lled with dielectric coolant DE, the top of capsule 46 can be covered by a closure 49 which may be sealed by epoxy or other self polymerizing resin.

I claim:

1. In a magnetically operated switch, particularly adapted to minimize the creation of unwanted ther-moelectric transients, a hollow bobbin, at least one sealedy capsule mounted within said hollow bobbin including means for supporting said sealed capsule therewithin, said sealed capsule `having switch elements therein at least one of which is movable in response to Va magnetic liux, a coil supported by said yhollow bobbin for providing magnetic flux for operation of said lone switch element, conductor members extending from said sealed capsule and electrically connected to the switch elements therein, contact members including means for supporting the same, a conductor connecting said c-onductor member and said contact member, at least one of such connections being at a juncture of dissimilar metals giving rise to the creation of an unwanted electrical transient upon heating of said juncture, said conductor being of small cross section as compared to the cross section of said conductor member and said contact member and substantially incapable of transferring `heat from said contact mem-ber to said conductor member, and :a fluid dielectric totally immersing all of said conductor members, conductors of small cross section and contact members for insuring substantially minimal temperature gradient between the conductors of small cross section and the conductor member and contact member connected thereto whereby any electrical transients created at said junctures will be effectively cancelled.

2. The invention of claim 1 wherein said bobbin is enclosed in a casing having said contact members embedded therein, and wherein said casing is provided with a closure against leaking of said liquid dielectric.

3. A magnetically operated switch particularly adapted to minimize the creation of -unwanted thermoelectric transients, said switch comprising a hollow bobbin, at least one sealed capsule mounted Within said bobbin including means for supporting said sealed capsule therewithin, said sealed capsule having switch elements thereinV at least one of which is movable in response to a magnetic flux, a coil supported by said hollow bobbin for providing magnetic ux for operation of said one switch element, conductor members extending from said sealed capsule and electrically connected to the switch elements therein, contact members embedded in said bobbin, a conductor connecting said conductor member and said contact member, at least one of such connections -being at a juncture of dissimilar metals giving rise to the creation of an unwanted electrical transient upon heating of said juncture, said conductor being of small cross section as compared to the cross section of said conductor member and said -contact member and substantially incapable of transferring heat from said imbedded contact member to said conductor member, and a fluid dielectric occupying the remain-der of the volume in said hollow bobbin for insuring substantially minimal temperature gradient between the conductors of small cross section and the conductor member and contact member connected thereto whereby any electrical transients created at said junctnres will be eiectively cancelled.'v

4. The invention of claim 3 wherein a closure is provided for said hollow bobbin to retain the dielectric coolant therewithin.

5. A magnetically operated switch comprising a hollow bobbin, at least one sealed capsule mounted within said bobbin including means for supporting said sealed capsule therewithin, said means comprising lands extending within said hollow bobbin and in engagement with said sealed capsule, said sealed capsule having switch elements therein at least one of which is mova-ble in response to a magnetic -ux, a coil supported by said hollow bobbin for providing magnetic ux for operation of said one switch element, conductor members extending from said sealed capsule and electrically connected to the switch elements therein, contact members embedded in said bobbin, a conductor connecting said conductor member and said contact member, said conductor being of small cross section as compared to the cross section of said conductor member and said contact member and substantially incapable of transferring heat from sai-d imbedded contact member to said conductor member, and a dielectric occupying the remainder of the volume in said hollow bobbin for insuring substantially minimal temperature gradient between the conductors of small cross section and the conductor member and contact member connected thereto.

6. Amagnetically operated switch comprising a hollo bobbin, at least one sealed capsule mounted within said 'bobbin including means for supporting said sealed capsule therewithin, said sealed capsule having switch elements therein at least one of which is movable in response to a magnetic ilux, a coil supported by said hollow bobbin for providing magnetic flux for operation of said one switch element, conductor members extending from said sealed capsule and electrically connected to the switch elements therein, contact members embedded in said bobbin, a conductor connecting said conductor member and said contact member, said conductor being of small cross section as compared to the cross section of said conductor member and said contact member and substantially incapable of transferring heat from said imbedded contact member to said conductor member, and a fluid dielectric occupying the remainder of the Volume in said hollow bobbin for insuring substantially minimal temperature gradient between the conductors of small cross section and the conductor member and contact member connected thereto, and a closure threaded to one end of said hollow bobbin. l

References Cited by the Examiner UNITED STATES PATENTS 2,643,282 v6/1953 Greene 174-15 2,889,424 6/ 1959 Glore et al. 200-87 3,171,918 3/1965 Killion 200-87 3,201,540 9/1965 McNamara 200-87 vBERNARD A. GILHEANY, Primary Examiner,

II, BAKER, Assistant Examiner. 

1. IN A MAGNETICALLY OPERATED SWITCH, PARTICULARLY ADAPTED TO MINIMIZE THE CREATION OF UNWANTED THERMOELECTRIC TRANSIENTS, A HOLLOW BOBBIN, AT LEAST ONE SEALED CAPSULE MOUNTED WITHIN SAID HOLLOW BOBBIN INCLUDING MEANS FOR SUPPORTING SAID SEALED CAPSULE THEREWITHIN, SAID SEALED CAPSULE HAVING SWITCH ELEMENTS THEREIN AT LEAST ONE OF WHICH IS MOVABLE IN RESPONSE TO A MAGNETIC FLUX, A COIL SUPPORTED BY SAID HOLLOW BOBBIN FOR PROVIDING MAGNETIC FLUX FOR OPERATION OF SAID ONE SWITCH ELEMENT, CONDUCTOR MEMBERS EXTENDING FROM SAID SEALED CAPSULE AND ELECTRICALLY CONNECTED TO THE SWITCH ELEMENTS THEREIN, CONTACT MEMBERS INCLUDING MEANS FOR SUPPORTING THE SAME, A CONDUCTOR CONNECTING SAID CONDUCTOR MEMBER AND SAID CONTACT MEMBER, AT LEAST ONE OF SUCH CONNECTIONS BEING AT A JUNCTURE OF DISSIMILAR METALS GIVING RISE TO THE CREATION OF AN UNWANTED ELECTRICAL TRANSIENT UPON HEATING OF SAID JUNCTURE, SAID CONDUCTOR BEING OF SMALL CROSS SECTION AS COMPARED TO THE CROSS SECTION OF SAID CONDUCTOR MEMBER AND SAID CONTACT MEMBER AND SUBSTANTIALLY INCAPABLE OF TRANSFERRING HEAT FROM SAID CONTACT MEMBER TO SAID CONDUCTOR MEMBER, AND A FLUID DIELECTRIC TOTALLY IMMERSING ALL OF SAID CONDUCTOR MEMBERS, CONDUCTORS OF SMALL CROSS SECTION AND CONTACT MEMBERS FOR INSURING SUBSTANTIALLY MINIMAL TEMPERATURE GRADIENT BETWEEN THE CONDUCTORS OF SMALL CROSS SECTION AND THE CONDUCTOR MEMBER AND CONTACT MEMBER CONNECTED THERETO WHEREBY ANY ELECTRICAL TRANSIENTS CREATED AT SAID JUNCTURES WILL BE EFFECTIVELY CANCELLED. 